McCarron, who signed with Buffalo as a free agent for a chance to start after four years as a backup in Cincinnati, completed just 3 of 6 for 12 yards during four series.

The 27-year-old didn't show any obvious signs of being hurt — he was hit hard from behind by Myles Garrett and sacked by Larry Ogunjobi — and the Bills didn't disclose his injury until the fourth quarter.

Allen, the No. 7 overall pick, out-performed McCarron and Peterman rallied the Bills (2-0) with a late touchdown pass to tight end Nick O'Leary.

Rookie Nick Chubb and Carlos Hyde had touchdown runs for the Browns (1-1).

The Bills have wanted to take a slow approach with Allen, letting him watch and learn behind McCarron and Peterman. However, those plans may have to be scrapped.

Peterman who started two games as a rookie in 2017, was 8 of 10 for 113 yards and a score.

Allen fired a 2-yard TD pass to Rod Streater in the second quarter and led the Bills on three scoring drives. He completed 9 of 13 passes for 60 yards and was sacked once.

Not only did he outshine McCarron, but he stole some of the spotlight from Baker Mayfield, the No. 1 overall pick making his home debut. Mayfield finished 7 of 13 for 75 yards.

Cleveland starting QB Tyrod Taylor didn't do much against his former team, completing 4 of 7 pass for 22 yards in four series. The Bills traded him in March to the Browns.

Allen, who was promoted to second-string earlier this week, replaced an ineffective McCarron with the Bills trailing 7-0 and led Buffalo on two scoring drives for a 10-7 halftime lead.

Allen badly misfired on his first pass attempt before settling in. Helped by a 22-yard run from Marcus Murphy, Allen took the Bills to the Cleveland 2. After two running plays were stuffed, Allen showed poise and precision with his TD pass.

Dropping back, he first avoided rushing Browns end Nate Orchard and then took several steps toward the line of scrimmage before threading his pass to Streater in the back of the end zone.

Stephen Hauschka kicked field goals of 33 and 53 yards for Buffalo.

After gaining just 50 yards rushing on 33 carries last week, the Browns put an emphasis on their running game in practice.

The extra work seemed to pay off as Cleveland ran for 63 yards on its opening possession, which ended with Hyde's 4-yard TD run.

NATIONAL ANTHEM

While a giant American flag was unfurled across the field, players lined up along both sidelines for the signing of "The Star-Spangled Banner" without the slightest hint of a protest.

INJURIES

Bills: Standout DT Kyle Williams limped off after hurting his right leg in the second quarter — another potentially serious injury for Buffalo.

Williams went down during a running play and as trainers ran onto the field to check on him, Taylor came over and checked on his former teammate. Williams walked gingerly to the sideline before heading to the locker room with trainers.

The 35-year-old Williams is one of Buffalo's leaders and the longest-tenured player on the roster.

Browns wide receiver Jarvis Landry and rookie cornerback Denzel Ward were both fined by the NFL for personal fouls in last week's game. Landry was assessed a $13,369 fine for unsportsmanlike conduct while Ward was punished with a $10,026 tab for taunting.